The present invention relates to a low-pressure casing for a brake booster for use in automotive vehicles comprising two casing shells sealingly interconnected, one of the two casing shells having a casing end wall close to the master cylinder, the other of the two casing shells having a casing end wall close to the brake pedal and each of the two casing shells having a substantially cylindrical circumferential casing section extending to the area of interconnection; and an axially movable wall sealingly subdividing the low-pressure casing into a low-pressure chamber and a working chamber.
In low-pressure brake boosters for automotive vehicles, the master brake cylinder is fitted to one casing end wall of the low-pressure casing, while the other end wall is fastened to the automotive vehicle, preferably to the splashboard. The brake forces which are transmitted onto the actuating piston of the master brake cylinder when braking will have to be re-transmitted as reaction forces from the master brake cylinder onto the point where the brake booster is fastened to the automotive vehicle. Taking into consideration that these comparatively high tractive forces take their course via the low-pressure casing, the low-pressure casing has so far been constructed with comparatively thick walls, which acts adversely to a generally desired reduction of the brake booster's weight.
A substantial reduction in weight by employing a thin-walled low-pressure casing construction may be achieved by having the tractive forces transmitted via separate tie elements which interconnect the two casing end walls, for instance, tie bolts as disclosed in German Patent DE-OS No. 2,845,794 , or a central reinforcement tube, as disclosed in U.S. copending application of J. Belart and F. Wienecke, Ser. No. 061,113, filed July 26, 1979, assigned to the same assignee as the present application. In any case, the sealing of the axially movavle wall at the points where these tie elements extend therethrough necessitates additional structural arrangements and represents a possible source of failure.